Hitherto, internal olefins are used in various applications such as a base oil for petroleum drilling oils, a raw material for detergents, a raw material for paper sizing agents, a base oil or raw material for lubricant and a raw material for chemicals.
When used for the above applications, the internal olefins are required to have the following properties.
For example, for use as a base oil for petroleum drilling oils, internal olefins having 16 or 18 carbon atoms are used. These olefins are required to have adjustable pour points and kinematic viscosities, and high biodegradability.
For use as a raw material for detergents, various internal olefins having about 10 to 19 carbon atoms are used. These olefins are often required to have a particularly high linear chain content in order to improve their biodegradability.
For use as a raw material for paper sizing agents, various internal olefins having about 10 to 30 carbon atoms are used. Also, these olefins are often required to have a high linear chain content.
For use as a base oil or a raw material for lubricant, various internal olefins having about 5 to 30 atoms are mainly used. These olefins are occasionally required to have controllable pour points and kinematic viscosities, and high linear chain content.
Internal isomerization of α-olefins using metal catalysts containing Pt, Ru, Ni, etc. supported on alumina, solid acid catalysts such as zeolites (e.g. ferrierite and SAPO) or clay, or their combined metal/solid acid catalysts are known and are already industrially in practice.
Most side reactions occurring in the internal isomerization of α-olefins using combined metal/solid acid catalysts include oligomerization, skeletal isomerization and cracking.
The number of the carbon atoms of the olefin increases upon oligomerization and decreases upon cracking.
In the skeletal isomerization, the number of carbon atoms does not change. However, linear olefins are converted into branched, tri-substituted or tetra-substituted olefins depending upon the position of the double bond.
Branched olefins are also produced by oligomerization or cracking.
Although some techniques utilize the above reactions as methods for producing internal olefins, since, in recent years, the products are utilized as raw materials for detergents, drilling oils, etc., biodegradability is considered particularly important. Techniques which yield poorly biodegradable branched olefins are not favored.
It is known that skeletal isomerization and internal isomerization occur in the isomerization of an olefin using a solid acid catalyst such as zeolite, e.g. H-ZSM-5 (for example, Non-Patent Document 1).
A method is also known in which only internal isomerization is selectively allowed to occur, preventing side reactions such as skeletal isomerization, by using a catalyst such as Cr/aluminophosphate (for example, Patent Document 1), ferrierite (for example, Patent Document 2) or NiO/ZSM-5 (for example, Patent Document 3).
Techniques are further known which employ supported catalysts of Pd, etc. or catalysts whose external surface acid sites are treated with silane.
However these techniques are mainly designed to improve catalytic performance. Few improvements, in process, are made that realize mild reaction conditions which prevent catalyst deterioration and the above-mentioned side reactions.
Patent Document 1:U.S. Pat. No. 4,593,146
Patent Document 2:U.S. Pat. No. 4,727,203
Patent Document 3:U.S. Pat. No. 6,054,629
Non-Patent Document 1:J. Catal. 92(1985)